Stages consisting of a number of individual foldable, movable stage sections are widely used in multipurpose rooms or areas of hotels, schools, and the like, wherein differing use activities for the rooms require that the stage be capable of rapid setup, takedown and storage. Several different foldable stage structures have been developed for this purpose. One example of a folding mobile stage is found in my prior U.S. Pat. No. 3,351,029, which is assigned to the same assigee as the present invention. Improvements of that prior invention so as to permit elevational adjustment are shown in U.S. Pat. Nos. 3,999,491 and 4,074,636 to Kermit H. Wilson, and assigned to the same assignee as the present invention. In these prior patents, the main support legs generally disposed beneath the center of the stage are interconnected to form a base frame, and hinge means including a plurality of hinge links connect the stage surface members to the base frame to permit them to be folded to a vertical storage position. Caster wheels are provided near the bottoms of the main support legs, connected to sleeves which may move telescopically upward or downward on the legs. Control linkages connect from the stage surface members to the sliding sleeves to cause the casters to retract when the stage is in its operable position, and to be extended beyond the main support legs so as to support the stage, when the stage is in its folded position, so that the stage can be wheeled away to a storage area. While this type of structure has been very successful in achieving its intended function, the present invention makes certain improvements which provide even greater rigidity, better alignment of the stage surfaces, and more convenient and secure folding of the stage in its storage position.
In the prior structure, the rigidity of the base frame formed by the interconnection of the main support legs was limited by the positioning of the sliding sleeves for the casters. Since the sleeves had to move up and down, the lowest cross brace between legs was approximately nine or ten inches from the floor, making the main support legs somewhat vulnerable to bending in case of improper use. Also, the use of sleeves over the leg tubes required a certain amount of looseness of fit so as to make sure there was no problem of movement of the sleeves due to a tight fit between parts. As a result, however, there was a certain amount of looseness in positioning of the legs, and this sometimes required positioning plates on the undersides of the stage surface members for lateral positioning of the tops of the legs to avoid slight lateral misalignment of the stage surface members. The loose fit of the sleeves also resulted in tipping of the sleeves against the legs when the weight of the stage was on the casters, causing a significant and not always predictable amount of friction as the sleeves would move up and down the legs during folding and unfolding. The friction would, of course, make folding and unfolding more difficult. The loose fit and tipping of the sleeves also caused the casters to be slightly off from vertical, increasing the wear on the casters.